Manufacture of magnetic alloy



-'WILLOUGHIBY STA'IHAI SMITH, OF

GABNETI, SEVENOAKS, AND WALTER FREDERICK RANDALL, OF EW'ELL,

Puma-Hum 23, 1931 nun-En STATES PATENT- OFFICE ENGLAND No Drawing. Application filed August 16, 1930, Serial No. 475,888,:11111 in Grea This invention relatesto improvements in the manufacture of magnet1c alloys compr1sing mainly lron and nlckel suitable for use in electrical signalling conductors and more particularly a method of annealing such alloys to develop a substantially constant permeability over their working range. It is customary in order to develop magnetic permeability to anneal a temperature varying between 700-900 G.- and above the critical temperature of the alloy, after which the alloy will be found to possess in weak fields a high permeability which increases with a rise in field strength. This property of variable however, undesirable where the alloy is to be used in the form of wires or tapes for the for the signals conductor, the perloading of signalling conductors since eflicient, transmission of electric should change as little as possible with the Earging strength of the prevailing magnetic According to one feature of the present invention magnetic alloys substantially free from carbon and 'comprising mainly iron and nickel are subjected to a high tempera-.

ture heat treatment until they are complete.

ly annealed, followed, after cooling, by a further treatment at a lower temperature which is at least 50 in excess of the magnetic change point of the alloy and does not exceed 700 C;

This double heat treatment, it has been found-produces an alloy having a nearly constant permeability in magnetic fields commonlymet within electric 1f ignalling sysvtems.

It is however, to bedistinguished from the double heat treatment, to which it is-customary to subject nickel-iron alloys in order to develop maximum permeability, the alloy undergoing first a heat treatment at an annealing temperature of the order of 1000 C. 01

' lowed, after cooling, by a further heating up to the magnetic transition temperature or cha nge point of the alloy and by rapid cooling at a predetermined rate.- s

In the heat treatment of the present inven,

these magnetic alloys at permeability is, w

. possess of manganese to is then fully BENCHAMS, NEWTONPOIPLEFOBD, HENRY JOSEPH mannrac'runn or MAGNETIC ALLOY t Britain June 22', 1929.

tion the alloys during their second heat treatment are heated to a temperature, which is appreciably in excess of the magnetic transi- The invention is especially concerned with nickel-iron alloys havmg a nickel content not greater than 50% and preferably within the limits of 30-45%. With such alloys the sec- 0nd heat treatment should be carried out'at a temperature which is still further, viz at least 100. in excess of the magnetic transition temperature.

Another object of this invention therefore,

is the production of nickel-iron magnetic alloys containing 30-45% nickel which not only constant permeability over a wide range of field strength, but have high specific resistance. I

Alloys in accordance with this feature of the invention comprise 30-45% of nickel, with the addition of one or more such elements as are adapted to increase the specific resistance of the alloy, the total content of of the alloy. Examples of suitable elements which may be added for increasing electrical resistance .such addition however not exceeding 10% Q In some cases itmay be necessary to add small quantities of upto 1% promote workability. v In the manufacture of an electrical sig= nalling conductor continuously loaded with wire or tape made from a nickel-iron allo the alloy 1s prepared by the usual metho sand. after casting reduced to wire or tape of the desired dimension. This wire or tape nEt im inrtant. The annealing temperature 1e and may be between 900 -1050G.

i8 varia eea e Wat rman mam annealed to'develop maximum known methods in this case by %nlckel content to the copper conductor with the known precautions to provide an adequate spacing between the magnetic layer and the copper, and

the loaded conductor is subjected to a further heat treatment at 500700 C.

The temperature of this second heat treat Temperature of magnetic transformation 500' The duration of this second treatment at this temperature depends upon the dimensions of the sample of wire or tape. In the case of a conductor loaded with wire or'tape of the usual dimensions, a heat treatment at 500+700 C. lasting for four minutes has been found to be sufiicient.

It has been found that after the heat treat- I ment at the high temperature, the annealed alloy should 'referably be strained slightly before it is su jected to the treatment at the lower tem erature. In the case of the manufacture o a continuously loaded conductor described above, the magnetic wire or tape is strained sufliciently during its application to the copper conductor. If the straining operation is omitted a longer heat treatment at 500-.700 O. is required.

The heat treatment necessary for the alloy itself is substantially similar to that described abovefor use in the manufacture of a. cable. The duration of the first anneal may-be longer and isdependent upon the thicknesso'f the sheet or; rodl The following examples illustrate how, after a first treatment .at annealing temperature, followed by a second treatment at -a lower temperature, the alloy, which after the first treatment ossesses a high permea- 1 eatlgnincreasing value with the strength of eld,

bility in weak fiel s of.

ally develops a constant or substantially constant permeability over a wide range of field strength.

' Example 1 An alloy comprising Percent Nickel 41.3 Iron Y 58.6. Manganese 0.1

gavethe following results after heat treat- (1) at -900' C. H-O. 001 gnaw-1000 H-OJS gausa=3400 (ii) at 900' C. H-0.001 gauss= 420 and 600' C. H=0.1 gauss= 420 H=0.3 gausiu- .420

'H- -OJ puas- 420 The specific resistance of the heat treated alloy was 70 microhms per cm.

Ewample 2 An alloy comprising Per cent Nickel 30.6 Iron 64.6 Chromium 4.8

gave the following results after heat treatment Y (1 at some. g 01 gauss= s20 =0.0 =0.5 gauss=2200 (11) at 900 C. H=0.001 gauss= 400 and 600 C. H =0.1 gauss= 400 H==0.8 gauss- 450 H=0.5 gausa- 560 The specific resistance of this alloy was 89.5- microhms per cm.

Example An alloy comprising gave the following result after being subject to the double heat treatment of this invention H=0.001 gauss=395 H=O.1 gauss=395 H=0.3 gauss=410 H=0.5 gauss=440 The specific resistance" of the heat treated alloy'was 82.5 microhms per cm.

Ewample 4 An alloy comprising Per cent Nickel 3 Iron Copper 10 gave the following results after being subjected to the double heat treatment of this invention.

H=0.001 gauss=350 H=0.1 gauss=360 H=0.3 gauss=4=10 H=0.5 gauss='440 The specific resistance of the heat treated alloy was 82 microhms per cm.

- A feature of the present specification is that it shows the existence of phase equilibrium conditions at 500-700 C. which differ entirely from the' uilibrium conditions at 900 0., The. attainment of equilibrium -at atemperature as low as 500700 .0. would be a very lengthy process if straightforward baking at that temperature was used. This .diflicul is overcome in ,the present invention by heating the metal to above the equilibrium point (i. e. to 900 C. from the work-hardened condition, and t en re-annealing for a short-period at the low temperature.

v What we claim is 1. Amethod for the heat treatment'of sub- Per cent Nickel 32.8 Iron 65.2 Manganese- 2.0 I

stantially carbon and cobalt free magnetic alloys comprising mainly iron and nickel which comprises subjecting the alloys to a heat treatment at atemperature to anneal completely the alloy, followed, after cooling,

7 by a second heat treatment at a lower temperature not exceeding 7 00 C. but not less than 50 in excess of the magnetic change temperature which exceeds the magnetic transition temperature of the alloy by at least 100 but does not exceed'700 C. a

3. A method for the heat treatment of sub stantially carbon free magnetic alloys comprising mainly iron and nickel having a nickel content up to 50%, which comprises subjecting the alloys to a heat treatment at a temperature to anneal completely the alloy,

.followed, after cooling and straining, by a second heat treatment at a lower temperature which exceeds the magnetic transition temperature of the alloy by at least 100 but does not exceed 700 C. 7

4. The manufacture of a loaded signalling conductor with a loading material compri's ingsubstantially carbon and cobalt free magnetic alloy comprising nickel and iron in which the loading material is subjected to a heat treatment'at a temperature to anneal it completely, prior to its application such as by winding to the conductor after which it is subjected to a second heat treatment at a lower tempearture not exceeding 700 C. but not less than 50 in excess of the magnetic change point of the alloy.

5. The manufacture of a loaded signalling conductor with a loading material comprising substantially carbon free magnetic alloy comprising nickel and iron in which the loading material is subjected to a heat treatment at a temperature .to anneal it completely, prior to its application by winding to the conductor when it is strained slightly, after which it is subjected to a second heat treatment at a lower temperature not exceeding 700 C. but not less than 50 in excess of the magnetic change point of the alloy.

6. A method for the heat treatment of substantially carbon and -cobalt free magnetic alloys comprising mainly iron and nickel having a nickel content between 30% and 50%, which comprises subjecting the alloys to a heat treatment at a temperature to anneal completely the alloy, followed, after cooling, by a second heat treatment at a lower temperature which exceeds the magnetic transition temperature of the alloy by at least 100 but is between 500700.

7. A method for the heat treatment of substantially carbon and cobalt free magnetic alloys comprising nickel and iron having a nickel content of 3O -50% which comprises subjecting the alloys to a heat treatment at a temperature to anneal completely the alloy, followed, after cooling, by a second heat treatment at a lower temperature which exceeds the magnetic transition temperature of the alloy by at least 100 but does not exceed 7 00 C.

8. A method for the heat treatment of substantially carbon and cobalt freemagnetic alloys comprising iron, 30-50% nickel, and not more than 10% of an element for increasin the electrical resistance, which comprises su jecting the alloys to a heat treatment at a temperature to anneal completely the alloy, followed, after cooling, by a second heat treatment at a lower temperature which exceeds the magnetic transition temperature of the alloy by at least 100 but does not exceed 700 C.

9. A method for the heat treatment of substantially carbon and cobalt free magnetic alloys comprising mainly iron, nickel and an element to increase specific resistance of the alloy and which goes into solid solution, which comprises subjecting the alloys to a heat treatment at a temperature to anneal completely the alloy, followed after cooling, by. a second heat treatment at a lower temperature not exceeding 700 C. but not less than 50 in excess of the magnetic change point of the alloy.

10. A method for the heat treatment of substantially carbon and cobalt free magnetic alloys comprising mainly iron, nickel and an element to increase specific resistance to the alloy and which goes into solid solution, which comprises subjecting the alloys to a heat treatment at a temperature to anneal 

